An increasing number of abdominal surgical procedures are being performed with laparoscopic techniques in order to avoid a large skin incision. Typically in laparoscopic surgery, a special needle (a needle similar to the pneumoneedles described in U.S. Pat. No. 4,808,168 and U.S. patent application Ser. No. 07/808,152, both of which are herein expressly incorporated by reference) is inserted through the skin, and used to inflate the abdominal cavity with an insufflating gas such as carbon dioxide (Co.sub.2). Once the abdomen is adequately dilated, the needle is removed and a rigid access tube or cannula with a diameter larger than the pneumoneedle (for example 5, 10 or 11 mm) is passed through the skin in the same location.
The access tube provides access for laparoscopes or other laparoscopic surgical tools such as the stapler described in U.S. Pat. No. 5,040,715 or the surgical clip appliers described in U.S. Pat. Nos. 5,084,057 and 5,100,420. To drive the access tube through the skin, the surgeon places a trocar in the lumen of the access tube to provide a sharp, leading edge for cutting tissue.
The art is replete with trocar devices, including those shown in U.S. Pat. Nos. 4,535,773, 4,601,710, 4,654,030, 4,902,280 and 4,931,042. Those trocars typically comprise an obturator with cutting surfaces for penetrating the skin, and a spring-loaded protective sleeve that surrounds the obturator. As these trocar devices are urged through the skin, friction with the skin causes the protective sleeve to slide proximally (rearwardly). After the access tube has penetrated through the skin, there is no longer friction between the protective sleeve and the skin, and the spring is designed to urge the protective sleeve distally (forwardly) to cover the cutting surfaces. Some of those trocars lock the protective sleeve in the forward position to reduce the risk of accidental puncture of the underlying organs.
These prior art trocars rely on a similar principle of operation: The friction or drag on the protective sleeve as the trocar is advanced through the skin pushes the protective sleeve back (proximally) to expose the cutting surfaces. Once the access tube has penetrated the skin, the drag on the protective sleeve is reduced and the sleeve accelerates distally (forwardly) under the bias of the spring to cover the cutting surfaces.
FIG. 1 illustrates a portion of a typical prior art trocar similar to the 10 mm Auto Suture Surgiport T.M., generally available from U.S. Surgical of Norwalk, Conn. That trocar includes an access tube 1, an obturator 2 and a shield 3. The shield 3 is biased distally to cover the obturator 2. The shield 3 comprises a generally cylindrical tube with a slightly rounded or angled end portion 4.
Existing trocars such as the trocar shown in FIG. 1 encounter problems because a significant amount of force usually must be applied to penetrate the skin (particularly the tough fascia). As a result of the significant insertion force, the trocar may continue to advance toward the underlying organs after it has penetrated the skin. Thus, the protective sleeve must "catch up" to the moving trocar point before the trocar reaches the underlying organs.
FIG. 2 illustrates another prior art trocar. This Figure generally illustrates a portion of trocar that is currently being sold in the United States under the name 10/11 mm Endopath.TM. (generally available from Ethicon of Somerville, N.J.). U.S. Pat. No. 5,066,288 to Deniega et al. describes a trocar similar to the trocar shown in FIG. 2. That trocar includes an access tube 5, an obturator 6 and a shield 7. The shield 7 is biased distally to cover the obturator 6. Unlike other trocars, the shield 7 of the trocar shown in FIG. 2 includes a bullet shaped end portion 8 comprising three semicircular lobes 9.
U.S. Pat. No. 5,066,288 states that the trocar restricts tissue trauma. However, like the trocar shown in FIG. 1, trocars similar to those shown in FIG. 2 also encounter problems because a significant amount of force is nevertheless required to penetrate the skin (particularly the tough fascia). Again, as a result of the significant insertion force, the obturator may continue to advance toward the underlying organs even after it has penetrated the skin.
FIGS. 3 and 4 illustrate yet another trocar similar to the trocar described in U.S. Pat. No. 4,654,030 to Moll. That trocar includes an access tube (not shown), an obturator 10 and shield 11 that is biased distally to cover the obturator 10. The obturator has a triangular base 12, and three generally equilateral triangular surfaces 13.
The shield 11 comprises three parabolically shaped bevels 14 which form a triangular shaped opening 15. The parabolically shaped bevels 14 intersect at three edges 16. While U.S. Pat. No. 4,654,030 states that the trocar shown in FIGS. 3 and 4 markedly reduces the force required to insert the trocar into body cavities, the trocar shown in FIGS. 3 and 4 is believed to suffer from several drawbacks including: (1) the shield 11 is believed to concentrate tissue trauma generally at the edges 16 during insertion into the body cavity resulting in undesirable tissue trauma at the incision site, (2) the shield 11 (particularly the edges 16) may become caught on tissue which restricts movement of the shield 11 relative to obturator 10, which is particularly undesirable after the obturator has pierced the abdominal wall; and (3) the edges 16 of the shield 11 may be relatively sharp and may expose the underlying organs to damage from contact with the edges 16 of the shield 11 itself.
U.S. Pat. No. 5,152,754 discloses a trocar comprising an obturator which retracts relative to the access tube just after the obturator pierces the tissue defining the body cavity. U.S. Pat. No. 5,152,754 is assigned to the assignee of the present invention.